The death toll from a mass shooting at a concert hall on the outskirts of Moscow Friday evening has risen to at least 133 people. At least another 145 others were reported injured.
The governor of the Moscow region said rescuers ended their search for victims late Saturday evening.
In his first televised address to the nation since the attacks took place, Russian President Vladimir Putin said Saturday afternoon that the Kremlin had arrested all four assailants directly involved in the shooting as well as seven others with suspected ties to the attack.
"All the perpetrators, organizers and those who ordered this crime will be justly and inevitably punished," Putin said.
"We will identify and punish everyone who stands behind the terrorists who prepared this atrocity, this strike against Russia, against our people."
Russia's interior minister said Saturday that all four suspected attackers are foreign citizens.
A U.S. official confirmed to NPR that the U.S. believes an Islamic State affiliate group known as Islamic State Khorasan Province, or ISIS-K, was responsible for the attack. The group, based in eastern Afghanistan, claimed responsibility for the attack on its Telegram channel late Friday.
U.S. intelligence officials also said they had warned the Kremlin earlier this month about a possible attack based on intelligence information.
"The U.S. Government had information about a planned terrorist attack in Moscow - potentially targeting large gatherings, to include concerts," Adrienne Watson, a spokesperson for the National Security Council, said in a statement on Friday.
Watson said the intelligence prompted the U.S. Embassy to issue a security advisory to Americans living in Russia, and share the information with Russian authorities in accordance with its longstanding "duty to warn" policy.
In his remarks on Saturday, Putin made no mention of ISIS-K, instead accusing Ukrainian authorities of trying to help the four assailants escape via Ukraine.
"They tried to hide and moved towards Ukraine, where according to preliminary data, a window was prepared for them on the Ukrainian side to cross the state border," Putin said.
Russian investigators said the assailants were detained in the western Bryansk region, not far from the border with Ukraine. Ukrainian officials have denied any involvement, with Ukraine's foreign ministry accusing Russian authorities of using the deadly assault to try to rally support for the Kremlin's war in Ukraine.
"ISIS bears sole responsibility for this attack," Watson, the NSC spokeswoman, said in a statement on Saturday. "There was no Ukrainian involvement whatsoever."
The attack began late Friday after camouflaged gunmen carrying automatic assault rifles burst into the Crocus City Hall — a large shopping and entertainment center on the western outskirts of Moscow. Concertgoers had gathered at the venue to see the veteran Russian rock band Piknik.
Harrowing video footage shows the men firing at bystanders as they attempted to hide or rush for the emergency exits. Some witnesses reported seeing the assailants pour a liquid on the concert hall's seating and curtains before setting it on fire. Additional footage released by Russian authorities shows the charred seating and debris from inside the venue.
NPR's Charles Maynes spoke to some of those who were inside the venue during the attack.
"The smoke kept coming and coming," said Alexei, a stagehand who told NPR's Charles Maynes he fled his third floor office to escape. He would only give his first name because of security forces present around the site.
"I'm still in a dream," he added, staring at the facade of the now-gutted concert hall.
Another venue employee, Josef, who refused to give a last name for similar reasons, said he was also still reeling from Friday night's events.
"You can imagine any terrorist, you can imagine anything. But to come through this main entrance. To kill the glass and to kill the people behind. I mean...no words. No words."
Putin declared Sunday a national day of mourning in Russia.
People across the country, meanwhile, have made spontaneous memorials with flowers, toys and candles to honor the victims. The local health ministry also said that more than 2,700 people donated blood in the Moscow region on Saturday to support the injured.
